A typical on-board power conversion apparatus for trains includes a circuit unit provided with an inverter circuit for converting DC power into AC power, a capacitor unit provided with a filter capacitor for stabilizing voltage input to an inverter circuit, and the like. The voltage of the DC power input to the inverter circuit for trains is, for example of the order of 1500 V. The filter capacitor thus requires high capacitance to accommodate the power, and when a molded capacitor with multiple capacitor elements molded to obtain the high capacity is employed as the filter capacitor, the molded capacitor weighs on the order of 25 to 60 kg. Such a heavy filter capacitor vibrates during train movement.
To address this issue, a conventional on-board power conversion apparatus for trains includes a capacitor unit in which a molded capacitor is accommodated and firmly fixed in a box-shaped housing constituted by a frame member, a reinforcing member, and the like to ensure strength high enough to resist the weight of the filter capacitor and its vibration over a long period of time (see, for example, Patent Literature 1). The housing is typically provided with a mounting plate on which the molded capacitor is fixedly mounted.